The remote detection and identification of chemical agents is an important research activity for state, local and federal governments, as well as for corporations and/or other interested individuals and groups. The threat of chemical warfare (CW) agents being used by rogue nations or terrorists, for example, is strong motivation for continuing the development of reliable early detection systems for such chemical agents. Since chemical agents are typically dispersed as aerosols or vapor to cover a wide area, an effective CW detection system should have a remote sensing capability with a high degree of sensitivity and selectivity in order to provide an early warning of the presence of a dangerous chemical agent.
Some existing chemical agent detection systems are based on laser technology, in order to identify the vibrational and rotational spectra of possible threat molecules in some way. Two detection methods in current use are known as Differential Absorption Lidar (DIAL) and Raman Back Scatter Spectroscopy. Methods such as these generally depend on the spectroscopic detection and analysis of back-scattered light signals from a distant target area, resulting from the incidence of illuminating laser beams on the potentially contaminated target area. The back-scattered signals are typically at very low power levels, however, and are generally closely spaced around the primary laser beam frequency. As such, the reliable detection of a specific gas molecule can be somewhat problematical and time-consuming with the use of conventional spectroscopic techniques.
Typically, high power lasers are used for illuminating a target area to induce a useful level of reflected back-scattered signals. Due to the low power levels and close spectral spacing of the back-scattered signals, however, the sensitivity and selectivity of the receiving apparatus of a CW detection system can be the major determining factors in the overall effectiveness and reliability of the system. That is, the detection and identification of a specific target agent, such as a nerve gas molecule for example, depends on the ability of a detection system to clearly and reliably distinguish the specific nerve gas spectrum from other reflected back-scattered signals.
Accordingly, it is desirable to provide a method and apparatus that selectively amplifies the back-scattered light signals of a specific target molecule to provide reliable detection and analysis of the target molecule. In addition, it is desirable to provide a method and apparatus with sufficient gain selectivity of back-scattered light signals to provide reliable detection and analysis of multiple target molecules simultaneously. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.